The present invention relates to an apparatus for detecting the penetration of volatile organic compounds through a material acting as a barrier. In particular, it relates to an apparatus which visually shows the residual life left in the material which is acting as a barrier.
It is desirable to protect humans from exposure to volatile organic compounds in various work environments, such as paint booths and laboratories, where such exposure may occur. Typically, this is accomplished by having the worker wear a respirator or some other filter device while working in the environment. One such respirator is described in U.S. Pat. No. 4,155,358. This respirator is a disposable valveless chemical cartridge respirator for filtration of vinyl chloride monomer having an end of service life indicator. Of particular interest is the end of service life indicator that is provided. The indicator undergoes a dramatic and distinct color change when the cartridge has expired. The indicator comprises specially prepared activated alumina granules coated first from a 1% solution of KMnO4, which is then reduced to what is believed to be MnO2, and then coated from a 0.55% solution of potassium permanganate. The indicator is viewed through the side wall of the cartridge all along the edge nearest the entrance to the cartridge. The initial color is purple and upon exposure to vinyl chloride, the potassium permanganate is reduced to manganese dioxide such that there is a slow, continuous color change from the purple to brown (the color of manganese dioxide). The problem with this type of indicator is that there is no way to determine how much life is left in the cartridge based on the color change. All that is known is that the cartridge life is beginning to or has expired.
U.S. Pat. No. 4,146,887 discloses an exothermic sensor which can be fitted in the cartridge adaptor or face piece cavity of the respirator. The sensor monitors the heat evolved during adsorption of the vapor or gas into the sensor""s adsorbent and triggers an alarm when the respirator cartridge has reached the end of its service life. As with the indicators described above, this sensor fails to let the user know how much life remains in the cartridge.
Other types of detection devices have also been described. In U.S. Pat. No. 4,205,043, a dosage badge for determining the exposure of firefighters to toxic gases is described. The dosage badge is affixed to the sleeve of a fireman""s overcoat. This badge comprises a plurality of paper discs impregnated with a color sensitive gas indicator chemical which is mounted in alignment with apertures in a plastic substrate by a pressure sensitive tape backing. The front face of the substrate is covered with a further strip of pressure sensitive tape, which is removed to initiate indication of gas dosage by the detector. Each of the respective discs changes color in response to respective predetermined dosages of a chosen toxic gas. At low dosages, all of the discs are of a first color. As the dosage increases the colors of the indicators change. However, as with the respirator technology, this dosage badge fails to indicate how much life would be left in an adsorbent bed. Rather, the badge merely indicates the level of exposure.
Alternatively, U.S. Pat. No. 5,376,554 describes an apparatus for detecting chemical permeation of hazardous or toxic chemicals through protective clothing. The apparatus and methods utilize a spectrochemical modification technique to detect the luminescence quenching of an indicator compound which upon permeation of the chemical through the protective clothing, the indicator is exposed to the chemical, thus indicating chemical permeation. In this method, the indicator compound is analyzed for luminescence quenching after the worker has been exposed to a toxic substance. The analysis requires the use of a portable luminescence monitor. This system would not be suitable when the wearer desires to know what, if any, residual life remains in the suit or if, while wearing the suit, the protective material has been spent.
An object of the present invention is to provide a residual life indicator which, through visual indication, and not color change, identifies how much life is left in an adsorbent material.
Another object of the present invention is provide a residual life indicator which is waterproof.
The present invention is directed toward a residual life indicator. The residual life indicator comprises a solid, surface active, waterproof support medium having a concentric pattern imprinted thereon. The concentric pattern comprises a center pattern and at least one outer pattern. An indicator dye spot is disposed within the center pattern of the concentric pattern. When the indicator dye is exposed to contaminants, the indicator dye spot visually moves toward the outer pattern.
The residual life indicator of the present invention is used for identifying how much life is left in an article containing an adsorbent bed. As the indicator dye spot grows toward an outer pattern, the user is able to visually determine how much life remains in the adsorbent bed and, thus, whether the device containing the adsorbent bed is still fit for its particular use. The residual life indicator does not require the use of external readers or instruments, thus making the residual life indicator inexpensive and easy to manufacture. Moreover, because there are no color changes involved, user error, which may result from color blindness, is minimized.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be obtained by means of instrumentalities in combinations particularly pointed out in the appended claims.